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Do Guinea Pigs Lose Weight In The Summer?

It’s always important to keep a close eye on your own health and your pets’, too! 

One of the most obvious indicators of an animal’s overall health is weight. 

Guinea pig owners need to monitor how much their guinea pigs will tell you if they are in a healthy range or need to gain or even lose a few grams.

But what if you’ve noticed your guinea pig tends to lose weight in the summer? 

In general, a guinea pig’s weight isn’t influenced in any significant way by the season. They do, however, grow in slightly thicker fur in the winter and shed much of this bulkier coat in the spring and summer. This will make your guinea pig appear slightly slimmer in the summertime by comparison. 

Keep reading to learn more about your piggy’s weight, the changing seasons, and when it is (and isn’t!) normal for their size to fluctuate. 

We’ll also go over related topics like causes of weight gain and loss in guinea pigs and what a healthy weight range looks like for guinea pigs of all ages. 

do guinea pigs lose weight in summer

Do Guinea Pigs Lose Weight in Summer?

While it is normal for a guinea pig’s weight to shift slightly from one week to the next, their weight loss and gain aren’t influenced much by the changing of the seasons. 

Your guinea pigs (ideally) will be living in a reasonably temperature-controlled enclosure anyway, so they aren’t going to have too much awareness of or much of a reaction to the seasons changing or the warm weather conditions outside.

However, one important thing to note here is guinea pigs do still grow in slightly thicker fur coats in the winter. 

This thicker coat won’t be heavy enough to cause your pigs’ weight to change, but it will likely give them the appearance of a slightly heftier build.

As a result, they will look a bit slimmer when they shed this winter coat in the spring and summer months. 

But again, the loss of this winter coat won’t be significant enough to affect your guinea pigs’ weight in any major way.

Learn more about guinea pig shedding in our guide to breeds and how much they shed.

What is a Healthy Guinea Pig Weight?

Before we move on to potential causes of weight loss and gain in guinea pigs and when to worry about their size-changing, it’s good to first establish what a healthy guinea pig weighs and looks like.

From birth, newborn guinea pigs typically weigh around 100 grams. 

Each week moving forward, they should gain around 30 to 60 grams. 

You’ll see this gradual weight increase over time. 

Upon reaching adulthood at around 6 months of age, they should weigh somewhere between 700 and 1,200 grams, depending on their sex.

Here is a general weight chart to follow month by month of your guinea pig’s growth. 

Guinea Pig’s Age (Months)Healthy Average Weight Range
Newborn80 to 120 grams
1 Month250 to 400 grams
2 Months450 to 700 grams
3 Months500 to 900 grams
4 Months600 to 950 grams
5 Months650 to 1,000 grams
6 Months+ (Adult)700 to 1,200 grams

Keep in mind males will typically lean towards the slightly heavier end of these weight ranges, while females will be slightly slimmer by comparison.

Severely underweight guinea pigs need to go to the vet right away. 

How Often Should You Weigh Your Guinea Pigs?

To monitor your guinea pig’s weight changes, it’s good to weigh them at least once or twice a month. 

However, weekly weigh-ins are even more ideal. 

This will give you the most accurate idea of your pet’s fluctuations in size to better pinpoint any potential health or dietary issues causing them to either gain or lose weight. 

To weigh your guinea pig, it’s best to simply use a kitchen scale measuring in grams. 

Digital scales are generally the most accurate. 

Because your guinea pig will likely wiggle around on the scale and make getting an accurate reading difficult, opt to place a small plastic container large enough to fit your guinea pig inside onto the scale first.

Next, start the scale to read zero with the container on top. 

Plop your piggy in the cozy container, so they aren’t able to mess with the reading, and check their weight in grams! 

Keep a small journal to track your pigs’ weight week to week (or, at the very least, month to month) to check for any major fluctuations.

Is it Normal For Guinea Pig Weight to Fluctuate?

guinea pig losing too much weight

Like all animals (including us humans), it is normal for weight to fluctuate slightly weekly and even day to day! 

However, while small weight changes are expected, larger fluctuations are often indicative of health or husbandry issues. 

So, what is a healthy amount of weight for your piggies to lose or gain from time to time?

Generally, changes in weight less than 25 grams or so in adult guinea pigs are expected from week to week and month to month. 

Your piggy’s weight will shift a bit depending on what they’re eating on a particular day, how much exercise they’ve been getting, and how old they are. 

However, adult guinea pigs who gain or lose more than 50 grams within a 2-to-4-week period should be closely monitored for further changes. 

Consulting with a vet is recommended if your guinea pig loses more than 50 grams OR weighs less than 700 grams if they are female or 900 grams if they are male.

Young, growing guinea pigs will gain a much more significant amount of weight during their first six months of life. 

Follow the aforementioned weight chart closely to ensure any of your juvenile guinea pigs are gaining weight at a safe and healthy rate. 

Weight loss of any kind during these first six months (at least more than 15 grams or more than 5% of their total body weight, anyway) often indicates dietary issues like nutritional deficiencies and should be taken seriously. 

Again, consult with a professional veterinarian if your juvenile guinea pig begins losing significant weight.

What Causes Guinea Pigs to Lose or Gain Weight?

Many potential factors will cause your guinea pig to gain or lose weight. 

Some of these are benign, while others are fatal if left untreated. 

This is why it is so essential for you to regularly monitor your piggy’s weight; they are such small animals that even a relatively small amount of weight loss or gain is often significant.

The leading overarching causes of significant weight loss or gain in pet guinea pigs are nutritional issues, husbandry issues, or illness. 

Teeth issues also frequently cause weight loss, as they will prevent your guinea pig from being able to eat normally and comfortably. 

There are many, many potential causes falling under these four general categories, but some of the most common ones include:

  • Vitamin C deficiency
  • Bacterial infections
  • Poor diet or poor quality pellets, veggies, or hay
  • Overbite, underbite, dental disease, or otherwise damaged teeth
  • Dehydration
  • Exposure to extreme temperatures or sudden temperature changes
  • Lack of access to food due to bullying and competition from more dominant pigs
  • Diabetes
  • Respiratory infection
  • Skin infection or irritation
  • Parasites
  • Stress (potentially from new cage mates or environmental changes)
  • Overfeeding or underfeeding
  • Recent surgical or other medical procedures
  • Urinary tract infection or bladder stones

If you’re keeping a journal to track your guinea pig’s weight changes, it’s good to record any health, diet, or general husbandry changes here. 

You’ll have plenty of information to pass on to your veterinarian so they know as much about your situation as possible. 

The more information your vet has about your guinea pig, the sooner you’ll be able to get a potential diagnosis and treatment plan moving forward to address the weight changes.

You might also be interested in knowing if your guinea pigs need pellets in their diet. Read our post here.

When to Worry About Your Guinea Pig Losing Weight

As we touched on above, it is normal for your guinea pig’s weight to fluctuate a bit over time. 

This weight change won’t be directly connected to or influenced by the seasons but rather several interwoven factors like: 

  • Diet 
  • Activity level
  • Age 
  • Sex
  • The overall quality of their care

Even if your pigs are fully-grown and generally healthy, knowing the warning signs of poor health to look out for is still important, so you know when things are more severe versus a normal weight fluctuation. 

If your piggy is under six months old and still growing, it should be consistently gaining weight and not losing 10 to 15 grams or so at a time. 

If any of your juvenile guinea pigs lose more than 15 grams (or more than 5% of their total body weight), contact your vet to make sure they aren’t developing any health or dietary issues. 

For adult guinea pigs, weight changes of around 25 grams or less are regular and expected from time to time. 

Check out how guinea pig age affects weight more in our guide here.

Even the healthiest animals have small weight fluctuations day by day depending on how much they’ve eaten, the time of day, and how active they’ve been recently.

Additionally, male guinea pigs will generally be heavier and larger than females. 

The typical female guinea pig should weigh 700 grams, while the average male guinea pig should weigh 900 or more. 

If your pigs weigh less, they’re likely not getting the nutrition they need to maintain a healthy weight or have developed an underlying health issue.

If your adult guinea pig has gained or lost more than 50 grams or so, it’s time to keep a closer eye on them and consult with a vet to determine the causes and a possible treatment plan moving forward.

Finally, if you notice any additional symptoms coinciding with the weight change, regardless of your guinea pig’s age or sex, this is also likely quite serious and indicative of health or dietary issues. 

Lethargy and loss of appetite (or very poor appetite) are the most dire symptoms to watch for.

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